Mechanical surface treatments cold-work the surface material, causing compressive residual stresses and, depending on the properties of the materials, often strengthening the surface against strain. One of the most common and versatile of the cold-working treatments is “shot peening.” In shot peening, the surface is bombarded with high-velocity shot, round metallic, glass or ceramic beads, discharged from a pneumatic nozzle. The resulting lightly hammered or “peened” effect places the surface in residual, preferably uniform, compression.
In one aspect, embodiments disclosed herein relate to a method of treating a surface and sub-surface of a metal substrate of a fluid end, wherein the fluid end comprises at least one lip between a longitudinal bore portion having a first diameter and a longitudinal bore portion having a second diameter. The method includes locating the lip within the longitudinal bore, wherein the lip comprises a radial dimension (R) not greater than 20 mils (0.508 mm), and directing accelerated shot having diameters on average not larger than about one-half the radial dimension (R) toward or near a surface of the lip at an angle between about 65 degrees and about 85 degrees relative to the longitudinal bore, thereby increasing compressive stresses in the metal substrate.
In other aspects, embodiments disclosed herein relate to a tool for cold-working a metal substrate of a longitudinal bore having a diameter less than about eight inches. The tool includes a deflector tip configured to direct accelerated shot having diameters on average not larger than 100 mils (2.54 mm) toward a surface of the metal substrate at an angle between about 70 degrees and about 85 degrees relative to the surface, thereby providing increased compressive stresses in the metal substrate.
In yet other aspects, embodiments disclosed herein relate to a method of cold-working a metal substrate within a longitudinal bore having a diameter less than about 36 inches. The method includes in at least one pass over a surface of the metal substrate, directing accelerated shot having diameters on average ranging between 50 mils (1.27 mm) and 100 mils (2.54 mm) toward the surface at an angle between about 70 degrees and about 85 degrees relative to the longitudinal bore, thereby increasing compressive stresses in the metal substrate. Then, in at least one pass over the surface of the metal substrate, directing accelerated shot having diameters on average ranging between 10 mils (0.254 mm) and 50 mils (1.27 mm) toward the surface at an angle between about 70 degrees and about 85 degrees, thereby decreasing a peak-to-valley profile of the surface of the metal substrate.